When Pharaoh hardened his heart against the first sign, notwithstanding the fact that it displayed the supremacy of the messengers of Jehovah over the might of the Egyptian conjurers and their gods, and refused to let the people of Israel go; Moses and Aaron were empowered by God to force the release of Israel from the obdurate king by a series of penal miracles. These מפתים were not purely supernatural wonders, or altogether unknown to the Egyptians, but were land-plagues with which Egypt was occasionally visited, and were raised into miraculous deeds of the Almighty God, by the fact that they burst upon the land one after another at an unusual time of the year, in unwonted force, and in close succession. These plagues were selected by God as miraculous signs, because He intended to prove thereby to the king and his servants, that He, Jehovah, was the Lord in the land, and ruled over the powers of nature with unrestricted freedom and omnipotence. For this reason God not only caused them to burst suddenly upon the land according to His word, and then as suddenly to disappear according to His omnipotent will, but caused them to be produced by Moses and Aaron and disappear again at their word and prayer, that Pharaoh might learn that these men were appointed by Him as His messengers, and were endowed by Him with divine power for the accomplishment of His will.

The Water of the Nile Turned into Blood. - In the morning, when Pharaoh went to the Nile, Moses took his staff at the command of God; went up to him on the bank of the river, with the demand of Jehovah that he would let His people Israel go; and because hitherto (עד־כּה) he had not obeyed, announced this first plague, which Aaron immediately brought to pass. Both time and place are of significance here. Pharaoh went out in the morning to the Nile (Exodus 7:15; Exodus 8:20), not merely to take a refreshing walk, or to bathe in the river, or to see how high the water had risen, but without doubt to present his daily worship to the Nile, which was honoured by the Egyptians as their supreme deity (vid., Exodus 2:5). At this very moment the will of God with regard to Israel was declared to him; and for his refusal to comply with the will of the Lord as thus revealed to him, the smiting of the Nile with the staff made known to him the fact, that the God of the Hebrews was the true God, and possessed the power to turn the fertilizing water of this object of their highest worship into blood. The changing of the water into blood is to be interpreted in the same sense as in Joel 3:4, where the moon is said to be turned into blood; that is to say, not as a chemical change into real blood, but as a change in the colour, which caused it to assume the appearance of blood (2 Kings 3:22). According to the statements of many travellers, the Nile water changes its colour when the water is lowest, assumes first of all a greenish hue and is almost undrinkable, and then, while it is rising, becomes as red as ochre, when it is more wholesome again. The causes of this change have not been sufficiently investigated. The reddening of the water is attributed by many to the red earth, which the river brings down from Sennaar (cf. Hengstenberg, Egypt and the Books of Moses, pp. 104ff. transl.; Laborde, comment. p. 28); but Ehrenberg came to the conclusion, after microscopical examinations, that it was caused by cryptogamic plants and infusoria. This natural phenomenon was here intensified into a miracle, not only by the fact that the change took place immediately in all the branches of the river at Moses' word and through the smiting of the Nile, but even more by a chemical change in the water, which caused the fishes to die, the stream to stink, and, what seems to indicate putrefaction, the water to become undrinkable; whereas, according to the accounts of travellers, which certainly do not quite agree with one another, and are not entirely trustworthy, the Nile water becomes more drinkable as soon as the natural reddening beings. The change in the water extended to "the streams," or different arms of the Nile; "the rivers," or Nile canals; "the ponds," or large standing lakes formed by the Nile; and all "the pools of water," lit., every collection of their waters, i.e., all the other standing lakes and ponds, left by the overflowings of the Nile, with the water of which those who lived at a distance from the river had to content themselves. "So that there was blood in all the land of Egypt, both in the wood and in the stone;" i.e., in the vessels of wood and stone, in which the water taken from the Nile and its branches was kept for daily use. The reference is not merely to the earthen vessels used for filtering and cleansing the water, but to every vessel into which water had been put. The "stone" vessels were the stone reservoirs built up at the corners of the streets and in other places, where fresh water was kept for the poor (cf. Oedmann's verm. Samml. p. 133). The meaning of this supplementary clause is not that even the water which was in these vessels previous to the smiting of the river was turned into blood, in which Kurtz perceives "the most miraculous part of the whole miracle;" for in that case the "wood and stone" would have been mentioned immediately after the "gatherings of the waters;" but simply that there was no more water to put into these vessels that was not changed into blood. The death of the fishes was a sign, that the smiting had taken away from the river its life-sustaining power, and that its red hue was intended to depict before the eyes of the Egyptians all the terrors of death; but we are not to suppose that there was any reference to the innocent blood which the Egyptians had poured into the river through the drowning of the Hebrew boys, or to their own guilty blood which was afterwards to be shed.